This invention relates generally to CCD (charge coupled device) imaging and particularly to a method for detecting blemishes contiguous to the perimeter of an image on a CCD.
U.S. Pat. No. 4,454,545 issued to R. A. Duschl discloses a CCD based inspection system.
U.S. Pat. No. 4,454,541 issued to R. A. Duschl discloses a system and method for detecting blemishes on the screen of a kinescope. Blemishes are detected by comparing the signal level on each CCD pixel with the average of the signals on the immediately adjacent pixels and generating a blemish signal when the difference exceeds a predetermined threshold.
U.S. Pat. No. 4,575,751 entitled "Method and Subsystem for Plotting the Perimeter of an Object" issued to R. A. Duschl, now U.S. Pat. No. 4,575,751, discloses a system for plotting the perimeter of an image cast onto a CCD. The image pixels immediately adjacent to the perimeter pixels are identified and their addresses held in memory irrespective of the orientation of the image and the size of the image.
U.S. application Ser. No. 663,699 entitled "Method for Avoiding Identifying Perimeter Variations As Blemishes in a CCD Image" filed on even date herewith by Edward Cohen discloses a method which can be used along with the present invention. The teachings of these patents and applications are incorporated herein by reference.
The systems described in the above-referenced application and patents are quite satisfactory for the purposes intended. However, difficulties sometime arise because a blemish in close proximity to the perimeter is identified as a portion of the perimeter and thus is not identified as a blemish which should result in the rejection of the object being inspected. For this reason, there is a need for a method for detecting blemishes in the close proximity of the perimeter of an image on a CCD. The present invention fulfills this long felt need.
The present invention is cast into the environment of detecting the perimeter of a black matrix on the inside surface of a CRT faceplate panel. This environment was selected when describing the present invention because the invention is an improvement of the inventions described in the referenced patents and patent applications and those inventions are described in that environment. Nevertheless it will be understood by those skilled in the art that the present invention is useful in detecting blemishes in the proximity of the perimeter of any image cast onto a CCD.